The present invention is related to polishing of materials, and in particular to the chemical-mechanical polishing (CMP) of dielectric layers or integrated circuits. Specifically, the present invention is directed to a method of securing a polishing pad to a platen used in the polishing of semiconductor wafers.
In the field of semiconductor manufacture, numerous integrated circuits are produced on round wafers through layers of wiring devices. During the process of forming layers and structures, the topography of the surface becomes increasingly irregular. The prevailing technology for planarizing the surface is chemical-mechanical polishing (CMP). In effect, this process planarizes the top layer of an integrated circuit prior to the depositing of another layer.
In CMP processes, the working layer of an integrated circuit is exposed to a moving polishing pad and a polishing slurry. In some systems, the polishing pad rotates about a fixed axis while the wafer rotates and moves across the pad. Pad properties and the polishing slurry have significant effects on polishing performance. Pads are engineered for specific properties such as stiffness, roughness, compressive modulus, flexural modulus and hydrophilic properties. Polishing slurries are also designed to enhance specific mechanisms during the polishing. These mechanisms are complex; however, in general the slurry contains chemicals that react with the deposited layer on the wafer, abrasives that mechanically cut (micro-machine) the layer, and complexing agents that prevent the removed material from precipitating or re-depositing on the wafer surface.
In most CMP applications, the polishing pad is affixed to a platen by an adhesive layer, typically a pressure sensitive adhesive (PSA). In this configuration, an operator removes the pad by pulling it off the platen, and subsequently cleaning the platen with a solvent, such as isopropyl alcohol. Since typical PSA materials have high peel strength, it can require significant force to overcome the pressure-sensitive-adhesive adhesion, thus increasing the changeover time. In addition, the operator could experience personal injury due to the poor ergonomics of the process, especially if the pad is stiff. Other prior-art systems have attempted to address these issues. U.S. Pat. No. 6,261,958 to Crevasse, et al. describes an apparatus that secures the pad without the use of adhesives by utilizing vacuum or electromagnetic force. U.S. Pat. Nos. 6,036,586 and 6,398,905 of Ward describe an improvement by using a permanent coating of a low-adhesion material such as polytetrafluoroethylene (PTFE). However, these prior-art improvements require either external equipment or modification to the machine and/or platen. Therefore, an improved method for affixing the pad to the platen is desirable.